Physiological Response of Tamarix ramosissima (Tamaricaceae) to a Biological Control Agent Authors: Craine, Evan B., Evankow, Ann, Wolfson, Katherine Bibee, Dalton, Kathryn, Swedlund, Holly, et al. Source: Western North American Naturalist, 76(3) : 339-351 Published By: Monte L. Bean Life Science Museum, Brigham Young University URL: https://doi.org/10.3398/064.076.0310 BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Complete website, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/terms-of-use. Usage of BioOne Complete content is strictly limited to personal, educational, and non - commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Downloaded From: https://bioone.org/journals/Western-North-American-Naturalist on 18 Feb 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado College Western North American Naturalist 76(3), © 2016, pp. 339–351 PHYSIOLOGICAL RESPONSE OF TAMARIX RAMOSISSIMA (TAMARICACEAE) TO A BIOLOGICAL CONTROL AGENT Evan B. Craine1, Ann Evankow1, Katherine Bibee Wolfson2, Kathryn Dalton1, Holly Swedlund1, Casey Bowen1, and M. Shane Heschel1,3 ABSTRACT.—Within the last century, the floristic composition of riparian communities in the Southwest has drasti- cally changed following introduction of the exotic tree Tamarix ramosissima. In an attempt to control Tamarix popula- tions, the tamarisk leaf beetle (Diorhabda carinulata) has been utilized as a biological control agent. Three years of data collection at our study sites along Fountain Creek (Fountain, CO) allowed us to characterize the response of Tamarix to invasion by the biological control agent. In analyzing data collected before, during, and after the beetle invasion, we observed a significant effect of foliar herbivory on Tamarix physiology and life history strategy. Associations between flower number and functional traits changed before, during, and after the beetle invasion. Before the invasion, repro- ductively fit individuals exhibited high stomatal conductance and used relatively more water. During and after the invasion, fit plants had higher foliar chlorophyll content, but conductance was not significantly correlated with fecundity. Tamarix responded to defoliation by increasing water use, which may have been an attempt to sustain photosynthate allocation to reproductive structures. Therefore, the leaf beetle may increase the water use of Tamarix during the growing season. RESUMEN.—Durante el último siglo, la composición floral de las comunidades ribereñas en el suroeste ha cambiado drásticamente tras la introducción del árbol exótico Tamarix ramosissima. En un intento por controlar las poblaciones de Tamarix, se ha utilizado al escarabajo de la hoja de tamariscos (Diorhabda carinulata) como control biológico. La colecta de datos durante tres años en nuestras áreas de estudio a lo largo de Fountain Creek (Fountain, Colorado) nos permitió caracterizar la respuesta de Tamarix a la invasión del agente de control biológico. Al analizar los datos obtenidos antes, durante y después de la invasión del escarabajo, observamos un efecto significativo de la herbivoría foliar en la fisiología y la estrategia de historia de vida de Tamarix. Las asociaciones entre el número de flores y los rasgos funcionales se modificaron antes, durante y después de la invasión de escarabajos. Antes de la invasión, los individuos reproductiva- mente aptos mostraban en los estomas una conductancia elevada y utilizaban relativamente más agua. Durante y después de la invasión, las plantas sanas mostraron un mayor contenido de clorofila foliar, pero la conductancia no se correla- cionó significativamente con la fecundidad. El Tamarix respondió a la defoliación mediante el aumento en el uso de agua, lo que pudo ser un intento para mantener la asignación de fotosintatos a las estructuras reproductivas. Por lo tanto, el escarabajo puede aumentar el uso del agua de Tamarix durante su estación de crecimiento. Species of the nonnative genus Tamarix Tamarix invasion is aided by both biotic (Tamaricaceae) are invasive trees or shrubs and abiotic factors. The invasive nature of within riparian ecosystems of the southwestern Tamarix has particularly benefited from an - United States (Thomaso 1998, DeLoach et al. thropogenic disturbance to riparian ecosys- 2003). Tamarix species aggressively invade tems with dam construction and flow regula- riparian ecosystems and can completely tion. Dams disrupt natural flood regimes and exclude native species by forming monocul- alter fluvial processes (i.e., stream bank ero- tures of dense stands with high leaf area (Sala sion and sediment deposition), which are et al. 1996). The implications of Tamarix integral to the establishment of many native competition with native species for water and riparian species (Fenner et al. 1985, Strom - light are widespread. For example, riparian berg et al. 1991, Auble et al. 1994, Merritt community structure and fluvial ecosystem and Cooper 2000, Mortenson and Weisberg processes are transformed following Tamarix 2010). With decreased flooding and low flows, introduction and establishment (Lovell et al. waterways downstream of dams can experi- 2009), and water table depth can be altered by ence higher salinity levels (Lee and Bell Tamarix monocultures (Johnson 1987). 1999, Havel et al. 2005), which aid in the 1Colorado College, Department of Organismal Biology and Ecology, 14 E. Cache La Poudre St., Colorado Springs, CO 80903. 2Denver Museum of Nature and Science, Denver, CO 80205. 3Corresponding author. E-mail: [email protected] 339 Downloaded From: https://bioone.org/journals/Western-North-American-Naturalist on 18 Feb 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by Colorado College 340 WESTERN NORTH AMERICAN NATURALIST [Volume 76 establishment of salt-tolerant species (e.g., water under dry conditions than the other Tamarix) and inhibit the establishment of salt- riparian species. Thus, Tamarix water use can sensitive native species (Siegle and Brock depend on local environmental conditions. 1990, Busch and Smith 1995, Shafroth et al. When Tamarix does transpire less effi- 1995, Lovell et al. 2009). Moreover, native ciently, high water use by Tamarix is largely riparian species that are sensitive to water due to the high leaf area index of Tamarix availability are negatively impacted by reduced communities compared to other riparian water table height from river diversions and populations (Sala et al. 1996). In areas of high flow regulations (Smith et al. 1991, Stromberg density or leaf area, Tamarix has the ability to et al. 1991). dry up springs, drain small ponds, and even Certain key biological characteristics have desiccate perennial streams (Johnson 1987). contributed to Tamarix invasibility. Tamarix Controlling Tamarix stands with high leaf disperses small, comose seeds in vast quanti- area may conserve water, although the vege- ties throughout the growing season (Merkel tation that replaces Tamarix will determine and Hopkins 1957, Warren and Turner 1975). the magnitude of water conservation (Shafroth Continuous seed dispersal results in complete et al. 2005). colonization of viable germination sites by Varying management techniques have been Tamarix seedlings, and Tamarix seeds are able utilized in attempts to control and manage to germinate in soils with high salinity levels Tamarix, with the hope of restoring riparian (Brotherson and Winkle 1986, Shafroth et al. ecosystems and reducing water lost through 1995, Sala et al. 1996). Early growth strate- evapotranspiration by Tamarix. Because Tamarix gies result in resource allocation to below- represents the sole genus from the family ground biomass, which augments the capacity Tamaricaceae in North America, biological of Tamarix to operate as a facultative phreato- control with the tamarisk leaf beetle Dio - phyte (Brotherson and Winkle 1986, Busch rhabda spp. (Coleoptera: Chrysomelidae) has et al. 1992). Overall, Tamarix growth and been considered a viable management tech- physiology allow it to potentially monopolize nique (Gaskin et al. 2004). The beetles feed by water resources in riparian systems (Sala et al. scraping away the cuticle to access mesophyll 1996). and vascular tissues within the leaves. To miti- As water availability has become an increas- gate water loss from damaged leaf tissues, ingly contentious issue in arid regions of the Tamarix abscises masticated leaves (Snyder et southwestern United States, concerns have al. 2010). Because of reductions in photosyn- been raised regarding Tamarix water use. thate production, this leaf loss can lead to Some studies have demonstrated that Tamarix Tamarix mortality. water use is among the highest of any phreato- Since the original introductions occurred, phyte in the southwestern United States the beetles have successfully spread from the (Brotherson and Winkle 1986), including na - original release